The answer is an Internet Gateway (IGW). This is correct because a public subnet must have a route table with a default route (0.0.0.0/0) pointing to an IGW, which enables bidirectional traffic between instances in the subnet and the internet. Without this route, even instances with public IP addresses remain isolated, as the VPC’s implicit router has no path to the outside world. On the AWS Certified Security Specialty SCS-C02 exam, this concept tests your understanding of VPC routing fundamentals and is often paired with a trap: many candidates mistakenly think a public IP or a NAT Gateway alone suffices, but a NAT Gateway only supports outbound traffic from private subnets. The essential components for a public subnet are actually three: the IGW, a custom route table with the 0.0.0.0/0 route to the IGW, and the subnet’s association with that route table. A quick memory tip: “IGW for in-and-out, NAT for out-only” — if you need inbound internet access, always look for the IGW.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A Security Engineer is designing a secure VPC architecture. Which THREE components are essential for creating a public subnet that can host a web server accessible from the internet?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Route table with a default route (0.0.0.0/0) pointing to the IGW
Option B is correct because a public subnet requires a route table that directs traffic destined for 0.0.0.0/0 to an Internet Gateway (IGW). Without this default route, instances in the subnet cannot send or receive traffic from the internet, even if they have public IP addresses. The IGW acts as the target for this route, enabling bidirectional communication between the VPC and the internet.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
VPN connection to on-premises
Why it's wrong here
Not required for internet access.
✓
Route table with a default route (0.0.0.0/0) pointing to the IGW
Why this is correct
Routes internet-bound traffic from the subnet to the IGW.
Related concept
Read the scenario before looking for a memorised answer.
✓
Security group allowing inbound HTTP/HTTPS from 0.0.0.0/0
Why this is correct
Allows web traffic from the internet to the web server.
Related concept
Read the scenario before looking for a memorised answer.
✗
NAT Gateway
Why it's wrong here
Used for private subnets to access the internet.
✓
Internet Gateway (IGW)
Why this is correct
Allows internet traffic to reach the VPC.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse a NATGateway with an Internet Gateway, mistakenly thinking a NAT Gateway can provide inbound internet access to a public subnet, when in fact it only supports outbound traffic from private subnets.
Detailed technical explanation
How to think about this question
An Internet Gateway (IGW) is a horizontally scaled, redundant, and highly available VPC component that performs network address translation (NAT) for instances with public IP addresses. When a route table entry points 0.0.0.0/0 to an IGW, the IGW translates the instance's private IP to its associated Elastic IP or public IP for outbound traffic, and reverse for inbound traffic. In real-world scenarios, failing to attach the IGW to the VPC or omitting the route table entry will cause the subnet to remain private, even if security groups allow inbound HTTP/HTTPS.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Infrastructure Security — This question tests Infrastructure Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Route table with a default route (0.0.0.0/0) pointing to the IGW — Option B is correct because a public subnet requires a route table that directs traffic destined for 0.0.0.0/0 to an Internet Gateway (IGW). Without this default route, instances in the subnet cannot send or receive traffic from the internet, even if they have public IP addresses. The IGW acts as the target for this route, enabling bidirectional communication between the VPC and the internet.
What should I do if I get this SCS-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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This SCS-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SCS-C02 exam.
Question Discussion
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